Project Summary/AbstractCxcl10 is a chemokine that mediates leukocyte migration during normal immune response. In cancers Cxcl10has been considered as a good prognostic marker correlated with tumor immune infiltrates and therapyresponse consistent with its normal function in cytotoxic immune response. As such Cxcl10 has been utilizedas an indicator of robust immune response to therapy in clinical trials and Cxcl10-based cancer therapy hasbeen proposed. Paradoxically Cxcl10 is associated with metastasis and poor patient survival in severalcancers including breast cancer suggesting that Cxcl10 may have a function of promoting cancer progression.The molecular context of this Cxcl10 oncogenic role is not well understood. This research team has identifiedCXCL10 as one of the inflammatory genes repressed by the ING4 tumor suppressor which suggested apotential inverse functional relationship. Preliminary studies from the PIs laboratory analyzed breast tumorgene expression datasets including METABRIC and found that CXCL10-high/ING4-low expression wassignificantly associated with reduced disease-free survival in patients. These data suggested that Cxcl10 mayexert an oncogenic effect in the context of ING4 deficiencies. Corroborating this Cxcl10 induced in vitromigration of ING4-deleted cells but not of ING4-intact cells. The use of inhibitors demonstrated that Cxcl10-induced cell migration required Cxcr3 (the receptor for Cxcl10) and the Gbg subunits downstream of Cxcr3 Gprotein-coupled protein receptor (GPCR) but not Gai. These data indicated a novel mechanism of theCxcl10/Cxcr3/Gbg axis that mediated migration of ING4-deleted cells and potentially metastasis. Based onthese data the hypothesis that Cxcl10/Cxcr3/Gbg signaling mediates metastasis of ING4-deficient cancerwas generated. The overall goal of the study is to unravel the mechanism of Cxcl10 oncogenic signaling. Totest the hypothesis for this Small Grants Program R03 proposal the specific aims will focus on Gbg signalingas it may present novel therapeutic opportunities. The specific aims are: 1) to identify the specific Gbgsubunits responsible for mediating Cxcl10-induced migration of ING4-deleted breast cancer cells in vitro and 2)to determine the role of Gbg in Cxcl10-induced metastasis of mammary tumors using mouse models. In mousemodels gallein (a Gbg inhibitor) and Gb/Gg gene deletion will be evaluated for inhibitory effects on Cxcl10-induced tumor metastasis. Impact: Up to 34% of breast cancers have been identified as ING4-deficient which iscorrelated with lymph node positivity and poor patient survival. Thus delineation of the Cxcl10/Cxcr3/Gbg/ING4signaling mechanism may have a broad impact on breast cancer treatment. If the proposed hypothesis is provencorrect the cell and mouse models in the study can further be used to test novel therapeutic agents targeting thepathway.